c++中-1是true呢还是false呢

 1 #include <iostream>
 2 
 3 using namespace std;
 4 void changeFlag(bool &flag);
 5 
 6 int main()
 7 {
 8     bool flag = true;
 9     changeFlag(flag);
10     if(-1000)
11         cout<<"-1 is true"<<endl;
12     else
13         cout<<"-1 is false"<<endl;
14 
15     
16     cout<<"flag = "<<flag<<endl;
17 
18     return 0;
19 }
20 
21 void changeFlag(bool &flag){
22     flag = !flag;
23 }